1. Technical Field
The present disclosure generally relates to a motor-driven booster type brake system and method thereof. More particularly, the present disclosure relates to a motor-driven booster type brake system and method thereof, which is configured to generate hydraulic pressure in a master cylinder through multiplication of force using a motor of a motor-driven booster to achieve vehicle braking
2. Description of the Related Art
The background art of the present disclosure is disclosed in Korean Patent Laid-open Publication No. 2010-0098847 (Laid-open Date: Sep. 10, 2010).
Typically, in a motor-driven booster type brake system, when a driver presses on a brake pedal, a pedal force sensor detects pedal force of the driver and an electronic control unit (ECU) drives a motor of the booster based on the detection result of the sensor to deliver a multiplied force to a master cylinder. The master cylinder delivers hydraulic pressure to wheel brakes, i.e. front and rear wheel brakes, based on the multiplied force delivered from the booster. Then, an electronic stability controller (ESC) adjusts the hydraulic force delivered to the front and rear wheel brakes according to a braking mode to permit suitable braking In other words, the ESC allows a brake oil to be supplied to the respective wheel brakes in a normal operation mode. However, in an anti-lock brake system (ABS) mode, that is, when a locking phenomenon occurs in at least one wheel, the ESC allows braking of the ABS to be performed by closing some of oil passages.
However, such a conventional motor-driven booster type brake system has a problem in that, when a vehicle is in an ABS mode, hydraulic pressure applied to the wheel brakes excessively increases or fluctuates in vehicle braking.
Specifically, when generating hydraulic pressure in the master cylinder using the motor-driven booster, the conventional motor-driven booster type brake system compares an actual hydraulic pressure output from the master cylinder with a target hydraulic pressure to adjust the hydraulic pressure of the master cylinder to be in a target range. In this case, however, if some oil passages to the wheel brakes are repeatedly closed or opened in an ABS mode, it is difficult to achieve rapid change of hydraulic pressure output from the master cylinder to provide a suitable pedal force to the respective wheel brakes, casing excessive pressure to be applied to the wheel brakes.
Namely, since the conventional brake system simply compares an actual hydraulic pressure output from the master cylinder with a calculated target hydraulic pressure and changes the motor-driven type booster according to the result of comparison, the brake system cannot rapidly and effectively cope with variation of desired pedal force to be imparted to each of the wheel brakes according to operation of the ABS, so that excessive pedal force is imparted to the wheel brakes or fluctuation or divergence of braking pressure occurs, as indicated by a waveform shown at a lower part of FIG. 1. Furthermore, such an excessive increase of hydraulic pressure can cause failure of the brake system.
In FIG. 1, a waveform shown at an upper part indicates variation of hydraulic pressure delivered from the master cylinder to the wheel brakes, and the waveform shown at the lower part indicates variation of hydraulic pressure imparted to the wheel brakes.